Wash the quinces and remove the hairs along the rind using a brush. Core them and place them in cold water to prevent them from darkening.
Chop the walnuts coarsely with a knife. Wash the raisins and dry them. In a bowl, mix together the walnuts, honey, raisins, cinnamon, lemon juice and grated lemon rind. Fill the quinces with the resulting mixture after placing a small slice of lemon rind on the bottom to plug it. Place them in a tray laid out with aluminum foil and cover with aluminum foil on top.
Bake at 356°F (180 °C) for 40-50 min. with the fan on. 10 min. before the end, remove the aluminum foil so they can gain a nice crisp. Cool them and sprinkle with powdered sugar.
Source: Bulgarian cuisine.
Notes: The cores of the quinces are really hard to remove so I've attached a photo of a tool that I use to core apples and other fruits to make it easier. Also be sure to have a very sharp knife at hand.
It's best to have the opening fairly wide so you can place more filling in them. The honey listed is enough as far as sweetness goes, I personally like to taste a bit of the sourness too. If you'd like them even sweeter you can pour on 1 tsp honey or more on top as well.